The invention relates to a valve having at least one pump connection, one tank connection, and one appliance connection and a valve piston positionable inside the valve housing, which piston separates the pump connection from the tank connection in at least one blocked position and which operates in conjunction with an energy accumulator, a self-adjusting fluid flow being controllable by means of a control device between the appliance connection and the tank connection.
Such valves are routinely used in so-called hydraulic load sensing systems or control means and operate there like a piston manometer, directing an unneeded pump feed flow back to the tank. In order to prevent leakages in the appliance circuit from raising the appliance pressure to the performance level of the pump and thereby possibly disabling the load sensing system, the load on the appliance connection to the tank is to be removed. Such load removal is currently effected in a cost-effective manner by use of aperture control means, the aperture preferably being integrated directly into the piston manometer or being used separately in a control unit which is part of the load sensing control mechanism.
A disadvantage of these known solutions with the aperture design feature is the pressure dependence of the volume flow draining to the tank. In the case of appliances whose volume flow is independent of load, proceeds by way of proportional valves, for example, this then results in constant slowing of the appliance with increase in the load pressure, something which has an especially negative effect in the case of appliances with a low volume flow.
On the basis of this state of the art the invention pursues the object of further improving known valves to the end that such valves will not be characterized by the disadvantages described, especially when employed in so-called load sensing systems. In addition, it is to be possible to reduce the valve cost efficiently and so that the valve occupies little space. The object as thus formulated is attained by means of a valve having the features specified in claim 1. Since, as specified in the descriptive portion of claim 1, the control device consists of a fluid flow controller integrated into the valve piston it is possible, in contrast with known valve solutions, to use the aperture design to reduce the volume flow to the appliance, independently of the load, by a constant value, so that proportional load-independent control is effected. The disadvantages of the state of the art as described, in the form of slowing of the appliance in particular, are thus reliably excluded. The solution with the fluid flow controller claimed for the invention can be cost effectively applied and space-saving installation in the valve itself is possible as a result of integration of the fluid flow controller into the valve box. Since the valve claimed for the invention has only a few structural components, reliability of operation is ensured which benefits the load sensing system as a whole.
Other advantageous embodiments are specified in the dependent claims.